Actually I was going to recommend route 9 and a couple small roads you can find from doing a maquest search. It's not too far from Harper's Ferry to Purcellville. I don't think it's all that adangerous and several of the organized rides use that route for weekends. There you can catch the W&OD trail, which is a paved former railroad bed that is smooth and wide and goes 55 miles. Yoi connecet qwith the Custis trail as someone mentioned and you are soon in DC with having to deal with very little traffic. Being a former rail line the hills are very gradual.